Antenna training and tracking protocol

ABSTRACT

A particular communications protocol is used for antenna training to accomplish directional communications in a wireless communications network. In some embodiments, pertinent information for various requests, responses, and status reports, is included in information elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 14/693,048, filed Apr. 22, 2015, which is a continuation ofU.S. patent application Ser. No. 12/229,667 entitled “Antenna Trainingand Tracking Protocol,” filed on Aug. 26, 2008, which claims priority toU.S. Provisional Application No. 60/969,505, filed Aug. 31, 2007, all ofwhich are hereby incorporated by reference in their entirety.

BACKGROUND

Some types of wireless networks, in particular those that operate in the60 GHz bands, use directional communications to mitigate intra-networkand inter-network interference between devices. The directionality ofthe transmissions and receptions are typically achieved through the useof multi-antenna phased arrays. To achieve directionality in aparticular direction, such arrays are ‘trained’ by transmitting a knownpattern, and processing the resultant signals received at each antennaof the receiving device to determine the parameters to use to achievedirectionality in that particular direction. If the devices are mobile,new antenna training may be frequently required to adjust the desireddirectionality by determining new parameters. Although coarse antennatraining procedures are available, to achieve high data rates fineantenna training must be done, and currently defined protocols do notprovide an efficient process for doing this.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention may be understood by referring to thefollowing description and accompanying drawings that are used toillustrate embodiments of the invention. In the drawings:

FIGS. 1A and 1B show a wireless network, according to an embodiment ofthe invention.

FIGS. 2A, 2B, and 2C show overall frame formats, according to anembodiment of the invention.

FIGS. 3A, 3B, and 3C show information elements for antenna training,according to an embodiment of the invention.

FIGS. 4 and 5 show a portion of a training session, according toembodiments of the invention.

FIG. 6 shows bi-directional antenna training, according to an embodimentof the invention.

FIG. 7 shows a flow diagram of communications using a protocol forantenna training, according to an embodiment of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures and techniques have not been shown in detail inorder not to obscure an understanding of this description.

References to “one embodiment”, “an embodiment”, “example embodiment”,“various embodiments”, etc., indicate that the embodiment(s) of theinvention so described may include particular features, structures, orcharacteristics, but not every embodiment necessarily includes theparticular features, structures, or characteristics. Further, someembodiments may have some, all, or none of the features described forother embodiments.

In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.Rather, in particular embodiments, “connected” is used to indicate thattwo or more elements are in direct physical or electrical contact witheach other. “Coupled” is used to indicate that two or more elementsco-operate or interact with each other, but they may or may not be indirect physical or electrical contact.

As used in the claims, unless otherwise specified the use of the ordinaladjectives “first”, “second”, “third”, etc., to describe a commonelement, merely indicate that different instances of like elements arebeing referred to, and are not intended to imply that the elements sodescribed must be in a given sequence, either temporally, spatially, inranking, or in any other manner

Various embodiments of the invention may be implemented in one or anycombination of hardware, firmware, and software. The invention may alsobe implemented as instructions contained in or on a computer-readablemedium, which may be read and executed by one or more processors toenable performance of the operations described herein. Acomputer-readable medium may include any mechanism for storing,transmitting, and/or receiving information in a form readable by one ormore computers). For example, a computer-readable medium may include atangible storage medium, such as but not limited to read only memory(ROM); random access memory (RAM); magnetic disk storage media; opticalstorage media; a flash memory device, etc. A computer-readable mediummay also include a propagated signal which has been modulated to encodethe instructions, such as but not limited to electromagnetic, optical,or acoustical carrier wave signals.

The term “wireless” and its derivatives may be used to describecircuits, devices, systems, methods, techniques, communicationschannels, etc., that communicate data by using modulated electromagneticradiation through a non-solid medium. The term “mobile” wireless deviceis used to describe a wireless device that may be in motion while it iscommunicating.

Various embodiments of the invention use a particular communicationsprotocol to request, perform, and acknowledge antenna training andtracking for directional wireless communications. As the terms are usedhere, ‘antenna training’ pertains to establishing new parameters toachieve directionality before new directional communications begin,while ‘antenna tracking’, pertains to adjusting the establishedparameters during ongoing directional communications to maintain properdirectionality.

FIGS. 1A and 1B show a wireless network, according to an embodiment ofthe invention. For convenience, a piconet controller PNC is shown as thenetwork controller, while wireless devices (DEV) labeled A, B, C, and Dare shown as being part of the network. However, other types of wirelessnetworks and network devices may also be used. For example, the networkcontroller may be an access point (AP), base station (BS), or any othertype of wireless network controller. The other wireless devices may bemobile stations (MS), subscriber stations (SS), STA's, or any other typeof mobile wireless network devices. In FIG. 1A, the PNC is showntransmitting signals to the network devices in a substantiallyomnidirectional manner (the radiation pattern is represented by thelarge circle). In FIG. 1B, the PNC is shown transmitting signals to thenetwork devices in a directional manner (the radiation patterns arerepresented by the teardrop shapes, although actual radiation patternmay exhibit other features such as sidelobes and backlobes). In asimilar manner, each of the mobile devices may transmit to the PNC in anomnidirectional manner, or in a directional manner with the direction ofthe transmission beam being toward the PNC. The radiation patterns fromthe mobile devices are not shown to avoid making FIG. 1B look overlycluttered, but may also be shown with a circular shape (omnidirectional)or a teardrop shape (directional). Each of the controllers and otherwireless devices may comprise various components, such as but notlimited to an antenna, a radio, a processor, a memory, software, and insome cases a battery to provide operational power.

FIGS. 2A, 2B, and 2C show overall frame formats, according to anembodiment of the invention. All begin with a preamble to permitreceiving devices to synchronize on the signal, and a header to describehow to interpret the remaining parts of the frame. The preamble and theheader are shown as physical layer convergence protocol (PLCP), butother protocol conventions may also be used. FIG. 2A shows a commonformat, with the header being followed by at least one protocol servicedata unit (PSDU) containing data to be exchanged between the twocommunicating devices. However, there is no provision for antennatraining in this format. FIG. 2B shows a frame devoted primarily toantenna training, with the header being followed by an antenna trainingsection containing multiple training sequences. FIG. 2C shows acombination of both, with a section containing training sequences, andalso at least one PSDU to exchange information. In some embodiments, thePLCP Header may contain one or more fields to indicate the presence orabsence of the Antenna Training section and the PSDU(s). Each PSDU mayalso contain at least one medium access control (MAC) header, containingmore information about the contents of a portion of the PSDU. In someembodiments, MAC headers may be used to exchange information aboutantenna training (but not the actual antenna training sequences),although other embodiments may differ in this respect.

In a typical sequence of events, a device may request antenna trainingwith another device with which it has established communications. Priorto such a request, the devices may be communicating with each otherthrough omnidirectional communications, or through coarse directionalcommunications. The antenna training may permit fine directional (narrowbeam) communications, which may in turn permit higher data rates withless interference with neighboring devices. The format of FIG. 2A may beused to request this training, by placing the request into the dataformat at an appropriate place, such as in the MAC header. A responsefrom the other device may also use the format of FIG. 2A, accepting orrejecting the request. Any necessary exchange of information, such asthe antenna capabilities of the two devices, may also use this format.

The format of FIG. 2B may be used for the actual antenna training. (Theformat of FIG. 2C may also be used for this, if there is otherinformation to exchange and the PSDU is the appropriate place toexchange it.) Within the Antenna Training section, known trainingsequences may be repetitively transmitted from the first device to thesecond device, using different antennas, combinations of antennas,and/or antenna parameters at both the first and second devices. Thereceiving device may determine which portion of the training sequenceswere received with the highest quality, and provide this informationback to the device that transmitted the training sequences. Byperforming this exchange of training sequences in both directions, thebest combination of antenna(s) and/or parameters may be determined, foruse in subsequent directional communications.

The format of FIG. 2C may be used for antenna tracking. Although fineantenna training may have already been performed, wirelesscommunications are subject to changing conditions that may affect thequality of the communications. For example, one of the wireless devicesmay be relocated, or an object may be moved between the two devices,causing an obstruction to, or reflections of, the signals. While the twodevices are communicating using the results of the previous antennatraining, they may also monitor the quality of those existingcommunications by repeating the training sequences. These new resultsmay then be used to adjust the antenna selection and/or antennaparameters, so that suitable quality in the communications may bemaintained.

Information regarding the antenna training may be exchanged through theuse of new information elements (IE) that have been created for thispurpose. Information elements, in general, are a particular dataprotocol that has been previously created to allow specializedinformation to be exchanged within an overall frame format, withouthaving to redefine the frame formats for each new type of information.Although the general format of IE's is known, the particular IE'sdescribed here have been created to exchange antenna traininginformation.

FIGS. 3A, 3B, and 3C show information elements for antenna training,according to an embodiment of the invention. Each of these three IE'sbegins with the standard IE format of an 8-bit Element ID field toidentify which type of IE it is, followed by an 8-bit Length field tospecify the length of this IE. For the remaining fields, the exampleIE's are each shown with a particular number of particular fields ofparticular lengths, and arranged in a particular order. However, otherembodiments may differ in the types of fields, the number of fields, thebit length of each field, and/or the order of the fields, provided thekey information is still present.

FIG. 3A shows an antenna capability information element (ACIE),according to an embodiment of the invention. The ACIE containsinformation about the antennas of the device transmitting the ACIE. Thistype of IE may be exchanged between two devices during discovery and/orduring association, and may be included in any suitable frame of thoseoperations. Following the standard Element ID and Length fields, a TXAntenna Type field may be used to indicate the type of antenna systemthe device has for transmission. For example, this field may indicate anon-trainable antenna (NTA), a switched beam antenna (SBA), or a phasedarray antenna (PAA). An NTA cannot be trained to transmit only in aparticular direction, so indicating an NTA in this field may mean thatthe antenna training activities can be skipped. In some embodiments, anNTA may provide omnidirectional transmission only, while in otherembodiments a directional antenna with a fixed direction may be used.

An SBA can be made to transmit or receive directionally in any ofseveral directions, but these directions are pre-defined and limited innumber. Although in some embodiments the pre-defined directions maycollectively encompass the whole 360-degree arc (for example, 8directions each covering a 45-degree arc), fine adjustments betweenthese directions are not possible with an SBA, and communicationsquality may vary within a single directional arc. In some embodiments,an SBA will have multiple antenna elements, each of which is physicallyconfigured to be directional in a different, fixed, direction.

A PAA has continuously-adjustable directionality. A PAA may containmultiple, mostly omnidirectional, antenna elements arranged in aparticular physical pattern, with means to provide a separate signal toeach element for transmission, or to receive a separate signal from eachelement for reception. The transmissions from each of these multipleantenna elements may combine in such a way as to produce an overalltransmission that is strong in one direction, and weak in the otherdirections. For receiving, the receptions from each of these multipleantennas may be collectively processed in such as way as to separate outthe signals from a particular direction, while ignoring the signals fromother directions. The particular parameters used to provide thetransmission signals or to process the received signals may determinethe direction and narrowness of these directional communications.

The field for Number of TX Antenna Elements may indicate how many suchantenna elements are available to be used for transmission. Thisinformation may be used, for example, to determine how many times atraining sequence is to be repeated, so that the performance of everyantenna element can be monitored. The fields for RX Antenna Type andNumber of RX Antenna Elements are similar to the equivalent fields fortransmission, except these parameters are only applied to the antennasfor reception. In many applications, the type of antenna and the numberof antenna elements will be the same for transmit and receive (becausethe same antenna system is used for both), but this format allows fordifferences between these two. For example, if eight antenna elementsare to be used for transmission, while only four of those antennaelements are to be used for reception, this format can accurately conveythat information. A Reserved field is also shown, which is currentlyunassigned but may be made available for future enhancements.

FIG. 3B shows an antenna training information element (ATIE), accordingto an embodiment of the invention. As described before for FIG. 3A, theTX Antenna Type and RX Antenna Type fields may be used to specifywhether these antennas are NTA, SBA, or PAA, respectively. The nextthree fields in FIG. 3B may be used to indicate the number of trainingsequences to be used in the antenna training, the length of each ofthese training sequences, and the size of the training blocks to be usedin the antenna training. Since multiple training sequences may betransmitted sequentially, this information may help the receiving deviceseparate the incoming data stream into the correct training sequences.Sequences and blocks are described later in more detail.

Sometimes the training process may be continued over multiple frames.The Continuation field indicates whether the training parametersdescribed in this IE are to be applied to initiating a new trainingprocess, or if they are a continuation of an ongoing training processthat was previously initiated. The Training Desired field indicateswhether the device transmitting this IE even wishes to engage in atraining process. If not, some of the other fields in this IE, such asthe training block size, and the number and length of trainingsequences, may be ignored. The Number of Iterations field indicates howmany iterations between the transmitter and receiver will occur duringthe antenna training process. Performing the antenna training over asequence of iterations may decrease the amount of time needed for thewhole antenna training process.

The Feedback Needed field indicates whether feedback is required fromthe device receiving this IE. If required, this feedback may be providedin the AFIE described later. The Cycle Rotation field may indicate theorder in which the training sequences are provided during the actualtraining. This is also described later. The Status field may indicate 1)a request for training, 2) acceptance or rejection of such a requestfrom another device, or 3) such training is not supported by thisdevice. The Reserve field is currently unassigned.

FIG. 3C shows an antenna feedback information element (AFIE), accordingto an embodiment of the invention. This IE may be included in a responseto an ATIE that indicated Feedback was needed. The Status field mayindicate a beam selection status for the transmitter of the device thatthis device is providing feedback to, such as: 1) a transmit beam isbeing selected, 2) the same transmit beam(s) as before should continueto be used, or 3) different transmit beam(s) than before should be used.The Type of Feedback field may be used to indicate what type of feedbackthis IE is providing. The Selected Beam Index field may be used when theother device's antenna type is an SBA, to indicate which transmit beamis being selected. This field may be used only if the Status fieldindicated a transmit beam is being selected. The Quantized TransmitterWeights field may be used when the other device's antenna type is a PAA,to indicate the parameters to be used in the calculations. As before, acurrently-unassigned Reserved field may also be included in the IE.

FIGS. 4 and 5 show a portion of a training session, according toembodiments of the invention. Following a preamble and header, thetransmitting device may transmit a series of training sequences (TS),with each training sequence containing a known data pattern, which thereceiving device may process in particular ways to obtain parameters forantenna directivity. Each transmitter antenna may transmit a separate TSto each receiver antenna. For example, if the transmitter has Nantennas, and the receiver has M antennas, a total of N×M trainingsequences may be transmitted to cover every transmitter/receiver antennacombination. The order in which the training sequences rotate throughthe antennas may be specified by the Cycle Rotation field of the ATIE ofFIG. 3B. The two orders are shown in FIGS. 4 and 5, in which TSorepresents a training sequence transmitted from transmitter antenna 0,TSi represents the training sequence transmitted from transmitterantenna 1, etc. In FIG. 4, the same transmitter antenna transmits the TSto each of the receiver antennas in turn, before repeating this processfrom the next transmitter antenna. In FIG. 5, the opposite rotationpattern is used, with each transmitter antenna in turn transmitting a TSto the same receiver antenna, before repeating the process for the nextreceiver antenna. A ‘cycle’ represents a single antenna on one devicecommunicating TS's with all the antennas of the other device, and wouldcontain M TS's in FIG. 4, or N TS's in FIG. 5.

The examples of FIGS. 4 and 5 show training sequences being transmittedin one direction, from a particular device to another particular device.However, antenna training may require transmitting training sequences inboth directions, from each device to the other device, so thatsubsequent directional communication may take place in both directions.

FIG. 6 shows bi-directional antenna training, according to an embodimentof the invention. Such training may take place in either an explicitmode, in which the training may be handled as a stand-alone event, or inan implicit mode, in which the training is embedded into othercommunications. In the explicit mode, two control frames, labeled hereas Request To Train (RTT) and Clear To Train (CTT), may be used toinitiate a training session. When two wireless network devices arealready associated with each other (e.g., a PNC and a DEV, though otherembodiments may use other combinations), either device may request atraining session by transmitting an RTT to the other. The receivingdevice may respond by transmitting back a CTT. Both the RTT and the CTTmay contain an ATIE to set up the specifics of the training session. Forthe purposes of this description, the device requesting the training,e.g., the device transmitting the RTT, is considered a ‘source’ deviceS, and the device responding to the request, e.g., the devicetransmitting the CTT, is considered a ‘destination’ device D. The labelS->D in FIG. 6 indicates the source device is transmitting trainingsequences to the destination device, while the label D->S indicates thedestination device is transmitting training-sequences to the sourcedevice.

The terms SIFS and MIFS indicate a short interframe space and a mediuminterframe space, respectively. These are scheduled delays between thetime one device stops transmitting and another device startstransmitting, to give the respective devices time to switch theircircuitry between transmit and receive modes. These specific delays arecommonly used in wireless transmissions, but their inclusion here shouldnot be interpreted as a requirement in various embodiments of theinvention unless so claimed.

If the destination device does not respond to the RTT, or if it respondsby transmitting a CTT that does not accept the request to train, thenthe indicated training session in FIG. 6 may be aborted withouttransmitting any training sequences. However, if the destination deviceagrees to the training by returning an appropriate CTT, then the twodevices may immediately begin exchanging training sequences as shown.TRN indicates transmission of multiple training sequence containingpredetermined data, which the receiving device may process in particularways to obtain parameters for antenna directivity. In some embodiments,each TRN may include all the contents of FIG. 4, or alternatively allthe contents of FIG. 5, but this specific content should not beconsidered a limitation on various embodiments of the invention unlessso claimed. The receiving device may respond to the TRN by transmittingan ACK to indicate it correctly received the training data. The ACK mayalso contain other useful information, such as but not limited to anAFIE such as that illustrated in FIG. 3C. In some embodiments, an ACK isnot required, if the Feedback Needed field of the ATIE from the sourcedevice so indicates. A single TRN, with its associated ACK (if the ACKis used) is referred to here as a training block. As seen in FIG. 6,two-way antenna training may be accomplished by transmitting thetraining sequences from the source device to the destination device, andthen from the destination device to the source device.

The antenna training process may be a repetitive process, which can berepeated multiple times to improve the results. Because of this,multiple blocks may be transmitted in the same direction, with eachsuccessive block intended to improve the resulting parameters fordirectional communications in that direction. In the same manner, theentire two-way process may be repeated, in increments labeled in FIG. 6as iterations. To reduce the potential length of the training session,the parameters may be checked periodically, such as at the end of eachiteration, or at the end of a specified number of iterations. If theparameters are suitable, the remaining iterations may be skipped.Similarly, the parameters may be checked at the end of each block, orthe end of a specified number of blocks. If the parameters are suitable,the remaining blocks in that iteration in that direction may be skipped.

As previously described, the explicit training mode may be triggered bythe RTT-CTT exchange between two devices, which may result in animmediate training session. However, an implicit training mode may betriggered without resorting to the use of control frames. For example,an ATIE (see FIG. 3B) may be included in another type of frame (e.g., abeacon, though other types of frame may be used), with the Status fieldset to request a training session. The responding device may place anATIE in the response (which may also be a beacon or other type offrame), with the Status field set to indicate acceptance of the request.In this manner, the request and acceptance of a training session may beembedded in existing communications that were initiated for otherreasons. Similarly, the actual training sequences may be embedded inexisting communications frames that were initiated for other reasons. Inthe implicit mode, the actual training (sequences, blocks, iterations,etc.) need not happen immediately after being agreed to, and may beincorporated into one or more subsequent scheduled communications.

The implicit mode may also be used for antenna tracking (as opposed toantenna training). For antenna tracking, parameters for directionalcommunications have already been established, and are being used. Butfurther checking of these parameters may be used to accommodate changesin the communications environment, such as but not limited to themovement of the communication devices or of intervening objects. Thesame overall process may be used for antenna tracking as for implicitantenna training. In general, the process for antenna tracking may beshorter than the process for antenna training, as fewer blocks oriterations may be necessary to fine-tune the signal.

FIG. 7 shows a flow diagram of communications using a protocol forantenna training in a wireless network, according to an embodiment ofthe invention. Entries on the left side of the flow diagram indicateoperations performed by the source device, while entries on the rightside indicate operations performed by the destination device. In flowdiagram 700, at 710 a source device may transmit a request for trainingto a destination device. This request may be in the form of a Request ToTrain control frame, or the request may be embedded in an informationelement in another type of frame. The destination device may receive therequest at 720, and at 730 extract any necessary training parametersfrom an information element in the request. Note: these trainingparameters are used to create and interpret the training sequences usedin the training process. These are different than thepreviously-mentioned communication parameters that are derived byperforming the training process, and that will be used to shape thesubsequent directional transmissions.

At 740 the destination device may transmit a response to the sourcedevice, which receives the response at 750. The response may be in theform of a Clear To Train control frame, or may be embedded in aninformation element in another type of frame. As before, trainingparameters may be extracted from an information element in the responseat 760. Now that both the source and destination devices have thenecessary information to perform antenna training in both directions,this bi-directional exchange of training sequences may begin at 770. Ifthe exchange is so configured, acknowledgments may be included in theexchange, and in some embodiments the acknowledgments will containanother information element indicating the current status of thetraining process. In other embodiments, the acknowledgement may beomitted.

The training process may be repetitive, with the same training sequencesbeing repeated multiple times in this training session. When thecommunication parameters that are derived from this process are deemedsufficient, as determined at 780, the training process may be terminatedat 790, even if additional training sequences were originally planned.

The foregoing description is intended to be illustrative and notlimiting. Variations will occur to those of skill in the art. Thosevariations are intended to be included in the various embodiments of theinvention, which are limited only by the spirit and scope of thefollowing claims.

1. (canceled)
 2. A wireless device for a user station (STA) including amemory and one or more processors, the one or more processors includingcircuitry, the circuitry having logic to: provide a request for antennatraining, wherein the request is included in a frame having a physicallayer convergence protocol (PLCP) header that includes an indication ofthe presence of antenna training fields; process a response to therequest, the response including an indication of which antenna trainingfield corresponds to a highest quality signal; and use the response todetermine directionality settings for an antenna.
 3. The device of claim2, wherein the request is separated from a preceding response by atleast a short interframe space (SIFS) interval.
 4. The device of claim2, wherein the response includes an indication of a type of feedbackprovided with the response.
 5. The device of claim 4, wherein theresponse includes feedback, within a feedback information element,indicating a quality of a transmission measured in the antenna trainingsequence.
 6. The device of claim 2, wherein the request and the responserepeat for a number of iterations to refine antenna weight values. 7.The device of claim 6, wherein the circuitry further has logic toprovide a first request in a first frame, receive a response to thefirst request in a second frame, and transmit a second request in thesecond frame.
 8. The device of claim 2, wherein the circuitry hasfurther logic to: provide an antenna tracking request, wherein theantenna tracking request includes an indication of the number oftraining fields requested for the antenna tracking.
 9. The device ofclaim 2, wherein the frame includes an indication of a length of anantenna training sequence.
 10. The device of claim 2, further includingat least one phased array antenna.
 11. The device of claim 10, furtherincluding at least one switched beam antenna.
 12. A non-transitorycomputer-readable storage medium that stores instructions for executionby one or more processors of a user station (STA) to perform operationscomprising: provide a first request for antenna training, wherein therequest is included in a frame having a physical layer convergenceprotocol (PLCP) header that includes an indication of the presence ofantenna training fields; process a response to the first request, theresponse including an indication of which antenna training fieldprovided the highest quality signal; and provide a second request forantenna training, subsequent to the response, wherein the second requestis separated from response by at least a short interframe space (SIFS)interval.
 13. The non-transitory computer-readable storage medium ofclaim 12, wherein the response includes feedback, within a feedbackinformation element, indicating a quality of a transmission measured inthe antenna training sequence.
 14. The non-transitory computer-readablestorage medium of claim 12, wherein the instructions further cause themachine to: provide an antenna tracking request, wherein the antennatracking request includes an indication of the number of training fieldsrequested for the antenna tracking.
 15. A user station (STA),comprising: a wireless communication device including a radio, aprocessor, and a memory, the wireless communication device to operate ina 60 GHz or higher frequency band to: provide a request for antennatraining, wherein the request is included in a frame having a physicallayer convergence protocol (PLCP) header that includes an indication ofthe presence of antenna training fields; and process a response to therequest, the response including an indication of which antenna trainingfield provided the highest quality signal and the response furtherincluding an indication of a type of feedback provided with theresponse.
 16. The apparatus of claim 15, further comprising at least twoantennas.
 17. The apparatus of claim 16, wherein at least one of the atleast two antennas is a non-trainable antenna.
 18. The apparatus ofclaim 15, wherein the request is separate from a preceding response byat least a short interframe space (SIFS) interval.
 19. The apparatus ofclaim 15, wherein the response includes feedback, within a feedbackinformation element (IE), indicating a quality of a transmissionmeasured in the antenna training sequence.
 20. A device including amemory and one or more processors, the one or more processors includingcircuitry, the circuitry having logic to: receive a request for antennatraining, wherein the request is included in a frame having a physicallayer convergence protocol (PLCP) header that includes an indication ofthe presence of antenna training fields; and provide a response to therequest within a short interframe space (SIFS) of receiving the request.21. The device of claim 20, wherein the response including an indicationof which antenna training field provided the highest quality signal. 22.The device of claim 21, wherein the indication is provided within afeedback information element (IE) that indicates a quality of atransmission measured in the antenna training sequence.